Question

Medal pls help!
On a true-false test, each question has exactly one correct answer: true, or false. A student knows the correct answer to 70% of the questions on the test. Each of the remaining answers she guesses at random, independently of all other answers. After the test has been graded, one of the questions is picked at random. Given that she got the answer right, what is the chance that she knew the answer?

Answer 1

1 What is the percentage of questions the student doesn't know the correct answer to?
2 What is the chance the student will pick the correct answer? (Hint: there are two options, true and false.)
3 So what is the expected percentage of questions the student will get right in total? (Include those she knows the answer to and those she doesn't know the answer to.)
4 Compare this with the proportion of questions she knew the answer to.

Answer 2

is it .7/10

Answer 3

oh ok...so it's .7plus the .5 of the questions she guessed
am i on the right track here

Answer 4

Yep that's the expected % of questions she'll get right.

Answer 5

thanks

Answer 6

(there's still the second part though but no problem)